The present invention relates to an image acquisition system, and more specifically, to an apparatus and method of scanning objects with a camera system.
Recent developments in xe2x80x9cover-the-deskxe2x80x9d scanning take advantage of combining the functionality of traditional paper scanning devices with that of a digital camera. Over-the-desk scanning generally refers to capturing images of hardcopy documents positioned on a desktop with a camera positioned above the desktop. These captured images are digitized for further processing and then displayed on a computer monitor. An example of such an over-the-desk scanning system is disclosed by Wellner in U.S. Pat. No. 5,511,148 entitled xe2x80x9cInteractive Copying System.xe2x80x9d
Over-the-desk scanning has many advantages over traditional scanning methods using devices such as flat-bed scanners, sheet-feed scanners and hand-held scanners that use contact scanning to reproduce high resolution images of documents. In general, contact scanning is limited to the scanning of flat objects, such as documents, and is often considered cumbersome to use because the document must be moved from its place of reading or the scanner must be moved relative to the document for scanning.
One advantage of over-the-desk scanning versus traditional contact scanning is that of convenience because it is not necessary to remove documents from their usual place of reading. This encourages a more casual type of scanning where the user is able to scan small amounts information from a document as it is encountered while reading, rather than making a note of its position in a document for scanning at a later time.
A second advantage is that the non-contact nature of over-the-desk scanning allows the capture of three-dimensional (3D) objects in addition to capturing two-dimensional (2D objects). Thus, human gestures, as well as physical media, may be captured by the over the desk scanning. For example, a pointing finger may be used to annotate a hardcopy document captured by the camera.
Over-the-desk scanning solutions are often implemented with consumer-level video cameras. Although the use of cameras to scan objects provide many advantages over traditional scanning methods, the use of consumer-level video cameras for document scanning is often limited by the resolution of the camera. Low-resolution cameras, such as consumer-level video camera, typically do not yield images with sufficient quality to enable successful document decoding using optical character recognition (OCR). For example, an OCR error rate under 1% may be achieved for 10-point Times Roman text scanned with a video camera by applying carefully created binarisation algorithms to camera images acquired at such low resolutions as 100 dots per inch (dpi). Below this resolution, the error rate and the time to recognize a page increases rapidly. Although some higher resolution cameras are available today, they are typically not cost effective for over-the-desk scanning solutions.
One approach used to improve low-resolution camera images is often referred to as xe2x80x9cmosaicingxe2x80x9d, xe2x80x9ctilingxe2x80x9d or xe2x80x9cstitchingxe2x80x9d. These techniques patch together several smaller low-resolution images to create a larger image having a higher resolution. Some overlapping between the smaller low-resolution images is required in order to patch them together to form one composite image. In general, mosaicing techniques yield an increased resolution that is roughly proportional to the number of images in the mosaic.
When mosaicing, the smaller low-resolution images may be obtained in a number of ways. For example, a camera may be moved relative to a large imaging area. The camera may be manually moved by the user or automatically moved by a translational device. Unfortunately, if the camera is panned and/or tilted, perspective distortions often need to be corrected.
Alternatively, mosaicing may be performed by moving an object to be imaged (e.g., document) with respect to the camera. This type of mosaicing is only feasible when the object can be easily moved. When used for scanning documents, this method requires non-intuitive and inconvenient interaction with the user, who must move his document so that all parts of it may be seen by the camera.
However, these two types of mosaicing techniques often result in transforming images by scaling, rotation or non-linear warping relative to each other. Subsequently, detection or calibration of the transformations and restoring the images to their undistorted coordinates must be performed before mosaicing can be obtained. Not only are these operations computationally intensive, but may degrade the quality of the images.
A third type of mosaicing technique can be achieved by moving an image sensor of a camera in a plane parallel to the image plane. This generally involves extensive modification or retrofitting of an existing consumer-level camera in order to mount the image sensor on a 2-axis translation device. The inability to use commercially available consumer-level video cameras is likely to increase the cost of an over-the-desk scanning system.
Another limitation of these types of mosaicing techniques is that the speed attainable by mosaicing systems is intrinsically limited by how fast a document or a camera may be moved. Moving the document or the camera is unlikely to be as efficient as moving light with the use of a periscope. An approach that shifts light is likely to improve the efficiency of a mosaicing system while enhancing the quality of over-the-desk scanning images and maintaining the cost feasibility of over-the-desk scanning solutions.
It is an object of the present invention to increase the resolution of an image scanned with a camera system.
It is also an object of the present invention to use a periscope to shift the view of a camera to various subsections of an object.
A further object of the present invention to obtain higher resolution images from a camera system at a higher frame rate than would be possible using other mosaicing techniques.
An optical system having a rotatable inner reflective surface and a plurality of outer reflective surfaces is described. The inner reflective surface is rotated about an axis of rotation to a plurality of predetermined positions by a driving mechanism. Each of the outer reflective surfaces together with the inner reflective surface positioned at one of the predetermined positions forms a reflective light path for enabling a camera to capture light rays originating from one of a plurality of object subsections.
Also described is an optical system having a plurality of reflective surfaces and a driving mechanism attached to one or more reflective surfaces. The driving mechanism rotates the attached reflected surfaces to a plurality of predetermined locations about an axis of rotation to form a reflective light path at each predetermined location for enabling a camera to capture light rays originating from one of a plurality of object subsections.
Additionally, a camera system is described. The camera system includes an image sensor, lens system, an inner reflective surface and a plurality of outer reflective surfaces. The reflective surfaces create a plurality of reflective light paths between the image sensor and the lens system. Each light path reflects light originating from one of the plurality of subsections of an object to be captured by the image sensor.
A method of scanning an object with a camera system is also described. The object includes N subsections. The camera system includes a periscope having an inner reflective surface and a plurality of outer reflective surfaces. The inner reflective surface is positioned at a first position about its axis of rotation such that light rays originating from a first subsection of the object travel through a first reflective path formed by the inner reflective surface and a first set of outer reflective surfaces. An image of the first subsection of the object is recorded. The inner reflective surface is positioned at a next position about its axis of rotation such that light rays originating from a next subsection of the object travel through a next reflective path formed by the inner reflective surface and a next set of outer reflective surfaces. An image of the next subsection of the object is recorded. The previous two steps are repeated until all subsections of the object are recorded. The images of the N subsections are combined to produce an image of the object.
An additional method of scanning an object with a camera system is described. The object includes N subsections and the camera system includes a periscope having a set of rotatable reflective surfaces. The set of rotatable reflective surfaces is positioned at a first predetermined position about an axis of rotation such that light rays originating from a first subsection of the object travel through a first reflective path. The image of the first subsection of the object is recorded. The set of rotatable reflective surface is positioned at a next predetermined position about the axis of rotation such that light rays originating from a next subsection of an object travel through a next reflective path. The image of the next subsection of the object is recorded. The previous two steps are repeated until all images of the N subsections have been recorded. Images of the N subsections are combined to produce an image of the object.
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.